Spinal plate assembly having locking mechanism

ABSTRACT

A spinal plate assembly comprising a base plate defining an opening adjacent at least one aperture for receiving a bone screw which attaches to spinal vertebrae. The aperture includes a seat and an annular groove having an end wall. The assembly comprises a locking mechanism having a split ring partially recessed within the annular groove and moveable between a locked condition partially blocking the aperture for retaining the screw in the seat and an unlocked condition radially deformable into the annular groove for permitting screw removal. The split ring has a proximal end and a distal end. The distal end is configured to engage the end wall of the annular groove. The locking mechanism comprises a rotating member retained within the opening of the base plate and having a notch configured to engage the proximal end of the ring to drive the ring toward the unlocked condition.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.16/576,027, filed Sep. 19, 2019, which is a continuation of U.S.application Ser. No. 14/993,369, filed on Jan. 12, 2016 (patented asU.S. Pat. No. 10,456,181), which is incorporated herein in its entirety.

FIELD OF THE INVENTION

The present invention relates generally to spinal plates used for fusingvertebrae in the treatment of spinal disorders, and more particularly toan improved locking mechanism within the plate assembly for securingbone screws in position after insertion and allowing for easy removaland readjustment.

BACKGROUND OF THE INVENTION

For over three decades plates have been used to increase stability ofthe spine following surgery to promote proper healing of injured ordamaged vertebrae caused by disease, trauma, spinal defect, accident orthe like, Conventional spinal plates are generally implanted duringsurgery by mounting to one or more vertebrae using bone screws. Theseplates often employ a locking mechanism to reduce the likelihood ofscrews disconnecting, reverse threading, backing out or otherwisepulling away from vertebrae in which they are mounted. Traditionallocking mechanism employ securing caps, cover plates, bearings, screwswith novel thread designs, and the like, in order to prevent the screwsfrom disengaging the vertebrae. However, many of these lockingmechanisms are ineffective, cumbersome, complicated and time consumingto apply, and unnecessarily expensive.

In addition, many of these locking mechanisms are unable to provideconvenient manipulation and readjustment of the bone screws and plateduring revision surgery. Those that do, require cumbersomeinstrumentation and complicated techniques to unlock and remove orreadjust. This increases the patient's chances of being exposed toinfection and, moreover, moves away from the industry's desire todecrease time spent in the operating room.

Therefore, there exists a need to provide a plate assembly having animproved locking mechanism that can cure some of the deficiencies in theprior art.

SUMMARY OF THE INVENTION

The present invention cures some of the deficiencies in the prior art byproviding a spinal plate assembly having an improved locking mechanismfor conveniently fixing screws in a locked position without the need forcumbersome hardware and complicated instrumentality. The improvedlocking mechanism of the present invention also enables a surgeon toquickly and easily unlock, remove and readjust the bone screw and plateafter locking has taken place.

In an illustrative embodiment of the present invention, a spinal plateassembly comprises a base plate defining a substantially circularopening between a pair of apertures for coupling adjacent to a spinalvertebra. The aperture includes a seat and an annular groove having anend wall. The assembly further comprises bone screws sized to beinserted through each aperture such that the bone screw sits within theseat of the aperture for engaging the spinal vertebrae. The assemblyfurther comprises a locking mechanism having a split ring partiallyrecessed within the annular groove of each aperture and moveable betweena locked condition and an unlocked condition. Each split ring has aproximal end and a distal end. The distal ends are configured to engagethe end walls of the respective annular grooves. The split rings areradially deformable within their respective annular grooves between thelocked condition partially blocking the aperture for retaining the bonescrews in the seat and the unlocked condition radially deformable intothe annular groove for permitting the bone screws to be removed from theapertures. The locking mechanism further comprises a rotating memberretained within the opening of the base plate having first and seconddiametrically opposed notches configured to engage the proximal ends ofthe split rings to simultaneously drive the split rings toward theunlocked condition. The rotating member includes a bore having across-section shaped to receive a conventional driving tool, therebyproviding faster and easier removal of bone screws without the need forcomplicated instrumentation.

These advantages of the present invention will be apparent from thefollowing disclosure and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of the spinal plate assembly having anintegrated locking mechanism shown in a “locked” condition according toan illustrative embodiment of the present invention.

FIG. 2 is a perspective view of the spinal plate assembly of FIG. 1 ,wherein the locking mechanism is shown in an “unlocked” conditionaccording to an illustrative embodiment of the present invention.

FIG. 3 is a top view of the spinal plate assembly of FIG. 1 , depictingthe elements that form the locking assembly in accordance with anillustrative embodiment of the present invention.

FIG. 4 is a top cross-sectional view of the spinal plate assembly ofFIG. 1 in a “locked” condition in accordance with an illustrativeembodiment of the present invention.

FIG. 5 is a side cross-sectional view of the spinal plate assembly ofFIG. 1 in a “locked” condition in accordance with an illustrativeembodiment of the present invention.

FIG. 6 is a top cross-sectional view of the spinal plate assembly ofFIG. 2 in an “unlocked” condition in accordance with an illustrativeembodiment of the present invention.

FIG. 7 is a side cross-sectional view of the spinal plate assembly ofFIG. 2 in an “unlocked” condition in accordance with an illustrativeembodiment of the present invention.

FIG. 8 is a perspective view of a spinal plate assembly having anintegrated locking mechanism shown in a “locked” condition according toan alternate embodiment of the present invention.

FIG. 9 is a perspective view of the spinal plate assembly of FIG. 8 ,wherein the locking mechanism is shown in an “unlocked” conditionaccording to an alternate embodiment of the present invention.

FIG. 10 is a top view of the spinal plate assembly of FIG. 8 , depictingthe elements that form the locking assembly in accordance with analternate embodiment of the present invention.

FIG. 11 is a side cross-sectional view of the spinal plate assembly ofFIG. 8 in a “locked” condition in accordance with an alternateembodiment of the present invention.

FIG. 12 is a top cross-sectional view of the spinal plate assembly ofFIG. 8 in a “locked” condition in accordance with an alternateembodiment of the present invention.

FIG. 13 is a top cross-sectional view of the spinal plate assembly ofFIG. 9 in an “unlocked” condition in accordance with an alternateembodiment of the present invention.

FIG. 14 is a side cross-sectional view of the spinal plate assembly ofFIG. 9 in an “unlocked” condition in accordance with an alternateembodiment of the present invention.

FIG. 15A is a perspective view of a spinal plate assembly having anintegrated locking mechanism shown in a “locked” condition according toyet another alternate embodiment of the present invention.

FIG. 15B is a perspective view of a spinal plate assembly having anintegrated locking mechanism including a screw shown in an “as inserted”condition according to an alternate embodiment of the present invention.

FIG. 15C is a perspective view of a spinal plate assembly having anintegrated locking mechanism including shown in an “unlocked” conditionaccording to an alternate embodiment of the present invention.

FIG. 16 is a top view of a spinal plate assembly of FIG. 15A, theassembly having an integrated locking mechanism including a screw shownin a “locked” condition according to an alternate embodiment of thepresent invention.

FIG. 17 is a cross-sectional view of the spinal plate assembly of FIG.15A in a “locked” condition in accordance with an alternate embodimentof the present invention.

FIG. 18 is a cross-sectional side view of the spinal plate assembly ofFIG. 15A in a “locked” condition in accordance with an alternateembodiment of the present invention.

FIG. 19 is a top view of a spinal plate assembly having an integratedlocking mechanism including a screw shown in an “as inserted” conditionaccording to an alternate embodiment of the present invention.

FIG. 20 is a top view of the spinal plate assembly having an integratedlocking mechanism including shown in an “unlocked” condition accordingto an alternate embodiment of the present invention.

FIG. 21 is a plan view of the bone screw in accordance with anillustrative embodiment of the present invention

FIG. 22 is a plan view of the bone screw in accordance with an alternateembodiment of the present invention.

DETAILED DESCRIPTION

Rotating Member and Flexible Element and Annular Groove

FIG. 1 is a perspective view of the spinal plate assembly 100 in a“locked” condition according to an illustrative embodiment of thepresent invention. FIG. 2 is a perspective view of the spinal plateassembly 100 in an “unlocked” condition according to an illustrativeembodiment of the present invention. The spinal plate assembly 100 inthese figures comprises: base plate 102, bone screw 104, lockingmechanism 106, and aperture 108. The base plate 100 of the illustrativeembodiment is preferably constructed from a biocompatible plastic,metal, metal alloy, or a combination thereof. The biocompatible metalsand metal alloys can be, for example, and without limitation, titanium,titanium alloy, stainless steel, cobalt chrome, or any combinationthereof. However, it will be clear to those skilled in the art, afterreading this disclosure, how to make and use alternative embodiments inwhich some of the elements of base plate 102 are made from a durablethermoplastic polymer, such as polyether ether ketone (PEEK).

It should be noted at this point of the disclosure that the lockingmechanism of the present assembly 100 is adapted for use with plates anddevices extending the spine and thoracic and lumbar regions, includingbut not limited to, cervical plates, thoracolumbar anterior and lateralplates.

In accordance with the illustrative embodiment, base plate 102 is anelongated structure having a lower surface 110 adapted to be placedagainst a plurality of vertebrae (not illustrated) and an opposite uppersurface 112. In order to couple base plate 102 to vertebrae, base plate102 has one or more apertures 108 therethrough for receiving one or morebone engaging fasteners, preferably bone screws 104. Bone screws 104 areimplanted through apertures 108 to fix base plate 102 to adjacentvertebrae or bony element. Bone screws 104, shown in FIGS. 21-22 ,comprise an elongated threaded shank portion 114 that extends downwardlyfrom an enlarged head portion 116 to fit inside aperture 108. The headportion 116 includes a tool recess 117, preferably a hexagonal or othernon-circular recess, configured to receive a driving tool having similarprofiled drive shaft (not shown). Preferably, shown in FIG. 21 , shapeof outside of head portion 116 of each bone screw 104 substantiallycorresponds to the shape of aperture 108, although this is not arequirement. Bone screw 104 includes a top 105, which may include ashoulder recess 107, shown in FIG. 22 .

The base plate 102 includes at least one locking mechanisms 106 moveablebetween “locked” and “unlocked” conditions. In the “locked” condition,as shown in FIG. 1 , bone screw head 116 is prevented from backing outof the aperture 108. In the “unlocked” condition, shown in FIG. 2 , bonescrew 104 is permitted to be removed from aperture 108.

FIG. 3 is a top view of spinal plate assembly 100 and elements that formlocking mechanism 106. Arranged within base plate 102 are apertures 108,each of which is sized and shaped to accommodate bone screw 104. Eachaperture 108 includes a seat 118 and an annular groove 120 having an endwall 122. Specifically, the figure shows a first apertures 108A sizedand shaped to receive a first screw 104A, while a second aperture 108Bis sized and shaped to receive second screw 104B (not shown). Base plateincludes at least one opening 109 adjacent the aperture 108 forreceiving at least a portion of locking mechanism 106. Preferably,opening 109 is defined between two aligned apertures 108. It should benoted at this point of the disclosure that one or more apertures 108 iscontemplated. In the case of one aperture (not sure) locking mechanism108 controls one screw 104. In the case of three apertures (not shown)locking mechanism 108 controls three bone screws 104 disposed withinthree separate apertures 108 simultaneously. Apertures 108 are shown inmore detail in the following figures, which will now be discussed. Itshould also be noted at this point of the disclosure that first aperture108A and second aperture 108B are substantially similar, albeit rotatedaround the central axis thereof from one other, and that same referencenumerals have been used to indicate same parts or elements throughoutthe various figures and specification. For the purpose of clarity, thefollowing discussion will use the generic word “aperture 108,” to referto both first and second apertures 108A, 108B.

FIG. 4 is a cross-sectional view of the spinal plate assembly of FIG. 1in the “locked” condition. In accordance with an illustrativeembodiment, locking mechanism 106 comprises one or more flexibleelements 124 and a moveable member 126 mounted therebetween. Preferably,moveable member 126 is a substantially cylindrical rotating member 126arranged with a pair of generally diametrically opposed notches 132,including a first notch and a second notch that are sized and shaped toengage flexible elements 124 and create biasing force to radially deformflexible elements 124 within respective annular grooves 120. Preferably,opposed notches 132 are cutouts extending within edge of rotatingmember. Flexible element 124 is preferably a deformable split ring 124,at least partially retained within annular groove 120 of aperture 108.Split ring 124 includes a proximal end 134 and a distal end 136.Proximal end 134 is configured to engage notch 132 of rotating member126, while distal end 136 is configured to engage end wall 122. Cutouts132 include extensions 133 to retain proximal end 134 of flexibleelement 124 and provide extra leverage for unlocking.

Split ring 124 is radially deformable into annular groove 120 as bonescrew 104 is inserted into aperture 108, allowing bone screw head 116 topass through and be seated in aperture 108. Once screw 104 is seatedwithin aperture 108, as shown in FIG. 5 , split ring 124 returns to“locked” condition partially blocking aperture 108 for retaining bonescrew head 116. In particular, split ring 124 rests adjacent top 104A ofbone screw 104. When bone screw 104 includes shoulder recess 104B, shownin FIG. 22 , split ring 124 rests adjacent shoulder recess 104 b, whichreduces overall height of plate 102.

FIG. 5 is a cross-sectional view of the spinal plate assembly of FIG. 1in the “locked” condition. Base plate 102 includes substantiallycylindrical opening 109 arranged between apertures 108, which extendsdownwardly to a seat 139. Seat 139 of opening 109 includes a bore 140extending axially therethrough. Rotating member 126 is generallycylindrical in shape and includes a substantially cylindrical head 128having a substantially cylindrical pin 129 extending downwardlytherefrom. Pin 129 is inserted within bore 140 of base plate 102 topivotally connect rotating member 126 within opening 109 of base plate.Pin 129 may also include a threaded shaft (not shown) for securing therotating member 126 within the opening 109. Head 128 of rotating member126 is preferably mounted flush with upper surface 112 of base plate 102so as to not intrude upon the body or working area of the base plate.Head 128 may also protrude (not shown) from the base plate 102 asdesired.

Head 128 of rotating member 126 includes an engaging portion 130 forreceiving a driver. Preferably, the engaging portion 130 is a recesshaving a cross-section 131 formed within head 128. Recess 130 allows adriving means, preferably a tool with a matching shaft (not shown), torotate member 126 clockwise about pin 129 within opening 109. Tool asdescribed in the illustrative embodiment has a hexagonal shaft formating with a hexagonal recess 130 of head 128, but any other matchingslotted, flat, triangle, square, star, rectangular, pentagonal, octagon,n-lobular, hexalobular, stardrive, Torx®, trilobular or other keyedshape is possible.

FIGS. 6 and 7 illustrate the spinal plate assembly of FIG. 2 in the“unlocked” condition to remove bone screw 104 from aperture 108.Rotating member 126 is rotated clockwise by driving means from “locked”to “unlocked” condition. As rotating member 126 is driven clockwise,notch 132 of rotating member 126 engages proximal end 136 of split ring124 to force distal end of split ring 124 to engage end wall 122 andradially deform into annular groove 120. Using driving tool (not shown),bone screw is then removed from aperture 108.

In accordance with the illustrative embodiment, rotating member 126 isconfigured to engage proximal ends 134 of first and second split rings124 so as to drive both rings 124 to the “unlocked” conditionsimultaneously.

Rotating Member Containing Flexible Element

FIG. 8 depicts a spinal plate assembly 200 having an integrated lockingmechanism shown in a “locked” condition according to an alternateembodiment of the present invention. FIG. 9 depicts a spinal plateassembly 200 with integrated locking mechanism shown in an “unlocked”condition according to an alternate embodiment of the present invention.The spinal plate assembly 200 shown in these figures comprises: baseplate 202, bone screw 104, locking mechanism 206, and aperture 208. Thebase plate 202 of the illustrative embodiment is preferably constructedfrom a biocompatible plastic, metal, metal alloy, or a combinationthereof. The biocompatible metals and metal alloys can be, for example,and without limitation, titanium, titanium alloy, stainless steel,cobalt chrome, or any combination thereof. However, it will be clear tothose skilled in the art, after reading this disclosure, how to make anduse alternative embodiments in which some of the elements of base plate202 are made from a durable thermoplastic polymer, such as polyetherether ketone (PEEK).

It should be noted at this point of the disclosure that the lockingmechanism of the present assembly 200 is adapted for use with plates anddevices extending the spine and thoracic and lumbar regions, includingbut not limited to, cervical plates, thoracolumbar anterior and lateralplates.

In accordance with the illustrative embodiment, base plate 202 is anelongated structure having a lower surface 210 adapted to be placedagainst a plurality of vertebrae (not illustrated) and an opposite uppersurface 212. In order to couple base plate 202 to vertebrae, base plate202 has one or more apertures 208 therethrough for receiving one or morebone engaging fasteners, preferably bone screws 104. Bone screws 104 areimplanted through apertures 208 to fix base plate 202 to adjacentvertebrae or bony element. Elongated threaded shank portion 114 of bonescrews 104, shown in FIG. 21 , extends downwardly from enlarged headportion 116 to fit inside aperture 208. Preferably, shape of outside ofhead portion 116 of each bone screw 104 substantially corresponds to theshape of aperture 208, although this is not a requirement.

Base plate 202 includes at least one locking mechanisms 206 moveablebetween “locked” and “unlocked” conditions. In the “locked” condition,as shown in FIG. 8 , bone screw head 116 is prevented from backing outof aperture 208. In the “unlocked” condition, shown in FIG. 9 , bonescrew 104 is permitted to be removed from aperture 208.

FIG. 10 is a top view of spinal plate assembly 200 and elements thatform locking mechanism 206. Arranged within base plate 202 are apertures208, each of which is sized and shaped to accommodate bone screw 104.Each aperture 208 includes a seat 218. Specifically, the figure shows afirst apertures 208A sized and shaped to receive first screw 104A, whilea second aperture 208B is sized and shaped to receive second screw 104B(not shown). Base plate 202 includes at least one substantially circularopening 209 adjacent aperture 208 for receiving at least a portion oflocking mechanism 206. Preferably, opening 209 is defined between twoaligned apertures 208, and includes a contact wall 220 and a diameter222. It should be noted at this point of the disclosure that one or moreapertures 208 is contemplated. In the case of one aperture (not sure)locking mechanism 208 controls one bone screw 104. In the case of threeapertures (not shown) locking mechanism 208 controls three bone screws104 disposed in three separate apertures 208 simultaneously. Apertures208 are shown in more detail in the following figures, which will now bediscussed. It should also be noted at this point of the disclosure thatfirst aperture 208A and second aperture 208B are substantially similar,albeit rotated around the central axis thereof from one other, and thatsame reference numerals have been used to indicate same parts orelements throughout the various figures and specification. For thepurpose of clarity, the following discussion will use the generic word“aperture 208,” to refer to both first and second apertures 208A, 208B.

FIG. 11 is a cross-section view of the spinal plate assembly of FIG. 8in the “locked” condition. Locking mechanism 206 comprises moveablemember 224, preferably a rotating member mounted within circular opening209 between pair of apertures 208, and flexible element 226. Circularopening 209 has a seat 245 and a bore 246 extending axially therethroughfor receiving rotating member 224. Rotating member 224 includes a head240 having a pin 244 extending downwardly therefrom. Head 240 isreceived within opening 209 of base plate 202 adjacent seat 245, suchthat pin 244 is received within bore 246. Pin 244 passes all orpartially through base plate 202 to couple rotating member 224 to baseplate 202. Rotating member 224 rotates within opening about pin 244. Pin244 may also include a threaded shaft (not shown) for securing therotating member 224 within the opening 209. Head 240 of rotating member224 is mounted flush with upper surface 212 of base plate 202 so as tonot intrude upon the body or working area of the base plate. Head 240may also protrude (not shown) from the base plate 202 as desired.

Head 240 of rotating member 224 includes an engaging portion 242 forreceiving a driver. Preferably, the engaging portion 242 is a recessformed within head 240. Recess 242 allows a driving means, preferably atool with a matching shaft (not shown), to rotate member 224 clockwiseabout pin 244 within opening 209. Tool as described in the illustrativeembodiment has a hexagonal shaft for mating with a hexagonal recess 242of head 240, but any other matching slotted, flat, triangle, square,star, rectangular, pentagonal, octagon, n-lobular, hexalobular,stardrive, Torx®, trilobular or other keyed shape is possible.

FIG. 12 is a cross-section view of the spinal plate assembly of FIG. 8in the “locked” condition in accordance with an alternate embodiment ofthe present invention. Head 240 of rotating member 224 includes a topsurface 232 and a bottom surface 234 and a groove 228 extendingcircumferentially therearound midway between top and bottom surface 234.Head 240 includes oppositely positioned wedging walls 230A, 230Badjacent circumferential groove 228, which are sized and shaped tocompress flexible element 226 between “locked” and “unlocked”conditions.

Flexible element 226 is preferably a deformable split ring 226 having afirst end 236, a second end 238, and a midpoint 240 substantiallybetween first and second ends. Spilt ring 226 includes a first portion242 between first end 236 and midpoint 240, and a second portion 244between second end 238 and midpoint 240. First and second ends 236, 238of split ring 226 are positioned within circumferential groove 228adjacent curved wall 230A, and midpoint 240 is positioned withincircumferential groove 228 adjacent oppositely curved wall 230B, suchthat ends and midpoint of split ring are compressed together betweenopposite wedging walls in the rotating member 224, thereby squeezing thesplit ring 226 to deform into the apertures 208. Specifically, first andsecond portions 242, 244 are deformed outwardly from circumferentialgroove 228 into apertures 208 in order to block screw heads 116 frombacking out of apertures 208. When bone screw 104 includes shoulderrecess 104B, shown in FIG. 22 , flexible element 226 rests adjacentshoulder recess 104 b, which reduces overall height of plate 202.

First and second portions 242, 244 of split ring 226 are compressedinwardly into circumferential groove 228 of rotating member 224 as bonescrews 104 are inserted into apertures 208, thereby allowing bone screwheads 116 to pass through and be seated in apertures 208. Once screws104 are seated within apertures 208, first and second portions 242, 244of split rings 226 return to “locked” condition partially blockingapertures 208 for retaining bone screw 104.

FIGS. 13 and 14 are cross-sectional views of the spinal plate assemblyof FIG. 9 in an “unlocked” condition in accordance with an alternateembodiment of the present invention. To achieve “unlocked” condition,rotating member 224 is rotated a quarter turn clockwise orcounterclockwise within opening 209, such that opposite wedging walls230A, 230B align with respective apertures 208 to block split ring 226from extending into apertures 208. In this position, first and secondportions 242, 244 of split ring 226 are retained between contact wall220 of opening 209, while ends 236, 238 and midpoint 240 of split ringare compressed between wedging walls 230A, 230B. Using driving tool (notshown), bone screws are then removed from apertures 208.

Loaded Rotating Member

FIG. 15A depicts a spinal plate assembly 300 having integrated lockingmechanism shown in a “locked” condition according to an alternateembodiment of the present invention. FIG. 15B depicts spinal plateassembly 300 having integrated locking mechanism shown in an “asinserted” condition according to an alternate embodiment of the presentinvention. FIG. 15C depicts spinal plate assembly 300 having integratedlocking mechanism shown in an “unlocked” condition according to analternate embodiment of the present invention. The spinal plate assembly300 shown in these figures comprises: base plate 302, bone screw 104,locking mechanism 306, and aperture 308. The base plate 302 of theillustrative embodiment is preferably constructed from a biocompatibleplastic, metal, metal alloy, or a combination thereof. The biocompatiblemetals and metal alloys can be, for example, and without limitation,titanium, titanium alloy, stainless steel, cobalt chrome, or anycombination thereof. However, it will be clear to those skilled in theart, after reading this disclosure, how to make and use alternativeembodiments in which some of the base plate 302 are made from a durablethermoplastic polymer, such as polyether ether ketone (PEEK).

It should be noted at this point of the disclosure that the lockingmechanism of the present assembly 300 is adapted for use with plates anddevices extending the spine and thoracic and lumbar regions, includingbut not limited to, cervical plates, thoracolumbar anterior and lateralplates.

In accordance with the illustrative embodiment, base plate 302 is anelongated structure having a lower surface 310 adapted to be placedagainst a plurality of vertebrae (not illustrated) and an opposite uppersurface 312. In order to couple base plate 302 to vertebrae, base plate302 has one or more apertures 308 therethrough for receiving one or morebone engaging fasteners, preferably bone screws 104. Bone screws 104 areimplanted through apertures 308 to fix base plate 302 to adjacentvertebrae or bony element. Elongated threaded shank portion 114 of bonescrews 104, shown in FIG. 21 , extend downwardly from enlarged headportion 116 to fit inside aperture 308. Preferably, shape of outside ofhead portion 116 of each bone screw 104 substantially corresponds to theshape of aperture 308, although this is not a requirement.

Base plate 302 includes at least one locking mechanisms 306 moveablebetween “locked” and “unlocked” conditions. In the “locked” condition,as shown in FIG. 15A, bone screw head 116 is prevented from backing outof aperture 308. In the “as inserted” condition, shown in FIG. 15B, bonescrew 104 is permitted to be inserted into aperture 308. In the“unlocked” condition, shown in FIG. 15C, bone screw 104 is permitted tobe removed from aperture 308.

FIGS. 16-18 illustrate spinal plate assembly 300 and elements that formthe locking mechanism 306 in a “locked” condition according to analternate embodiment of the present invention. In particular, FIG. 16 isa top view of spinal plate assembly 300, FIG. 17 is a cross-sectionalview of the spinal plate assembly, and FIG. 18 is a side cross-sectionalview of the spinal plate assembly. These figures illustrate twoapertures 308 arranged within base plate 302, each of which is sized andshaped to accommodate bone screw 104. Each aperture 308 includes a seat318 for receiving head portion 116 of bone screw 104 thereon.Specifically, apertures 308 include a first apertures 308A sized andshaped to receive first screw 104A, and a second aperture 308B is sizedand shaped to receive second screw 104B (not shown). Base plate 302includes at least one substantially S-shaped opening 309 extendingbetween and partially around apertures 308A, 308B. Opening 309 has aseat 348 and a bore 350 extending axially therethrough. Opening 309further includes a contact wall 320 and a pair of pockets 322 recessedwithin the contact wall 320.

Locking mechanism 306 comprises moveable member 324, preferably arotating member mounted within opening 309, and one or more flexibleelements 326. Rotating member 324 includes a substantially S-shaped mainbody 325 having a pin 346 extending downwardly therefrom 346. Main body325 includes a flex section 328 and a pair of curved screw engagingsections 330 at opposite ends thereof. Main body 325 is received withinopening 309 of base plate 302 adjacent seat 348, such that pin 346 isreceived within bore 348. Pin 346 passes all or partially through baseplate 302 to couple rotating member 324 to base plate 302. Rotatingmember 324 rotates within opening 309 about pin 346. Pin 346 may alsoinclude a threaded shaft (not shown) for securing the rotating member324 within the opening 309. Main body 325 of rotating member 324 ismounted flush with upper surface 312 of base plate 302 so as to notintrude upon the body or working area of the base plate. Main body 325may also protrude (not shown) from the base plate 302 as desired.

Main body 325 of rotating member 324 includes an engaging portion 344for receiving a driver 344. Preferably, the engaging portion 344 is arecess formed within flex section 328 of rotating member 324. Recess 344allows a driving means, preferably a tool with a matching shaft (notshown), to pivotally rotate rotating member 324 counterclockwise aboutpin 346. Tool as described in the illustrative embodiment has ahexagonal shaft for mating with a hexagonal recess 344 of flex section328, but any other matching slotted, flat, triangle, square, star,rectangular, pentagonal, octagon, n-lobular, hexalobular, stardrive,Torx®, trilobular or other keyed shape is possible.

Flexible elements 326 are a pair of loaded members 326 each partiallyretained within pockets 322 of opening 309 and moveable between a“locked” condition and an “unlocked” condition. Loaded members 326 arepositioned within respective pockets 322 so as to apply constant forceto screw engaging sections 330 of rotating member 324. In the “locked”condition, loaded members 326 extend outwardly from pockets 322 drivingthe rotating member toward apertures 308 and away from contact wall 320.In this condition, rotating member 324 is forced to rotate clockwisecausing screw engaging sections 330 to at least partially coverapertures 308 to prevent bone screws 104 from backing out of apertures308.

FIG. 19 is a top view of the spinal plate assembly 300 and elements thatform the locking mechanism 306 in an “as inserted” condition accordingto an alternate embodiment of the present invention. Each curved screwengaging sections 330 includes a leading edge 340, which engages withbone screw 104 and pushes rotating member 324 outwardly away fromaperture 308 as bones screw 104 is inserted into aperture 308. In thiscondition, rotating member 324 is forced to rotate counterclockwise suchthat screw engaging portions 330 force loaded members 326 to compresswithin pockets 322 and deform toward contact wall 320 allowing bonescrew 104 to be seated in aperture 308. When bone screw 104 includesshoulder recess 104B, shown in FIG. 22 , screw engaging portion 330rests adjacent shoulder recess 104 b, which reduces overall height ofplate 302.

FIG. 20 is a top view of the spinal plate assembly 300 and elements thatform the locking mechanism 306 in an “unlocked” condition according toan alternate embodiment of the present invention. In this position,rotating member 324 is further rotated, preferably by the driving means,toward a “capture point”, which retains rotating member 324 in an“unlocked” condition. Using driving tool (not shown), bone screws 104are then removed from apertures 308.

It is to be understood that the disclosure describes a few embodimentsand that many variations of the invention can easily be devised by thoseskilled in the art after reading this disclosure and that the scope ofthe present invention is to be determined by the following claims.

What is claimed is:
 1. A spinal plate assembly comprising: a base platedefining an aperture for receiving a bone screw, the aperture comprisinga seat and an annular groove; a deformable split ring having a proximalend, a distal end, and a curved portion between the proximal and distalends, the split ring overlying the aperture in its unbiased lockedposition, the curved portion of the split ring at least partiallyretained within the annular groove of the aperture and adapted to beflexed away from the aperture when the bone screw is being insertedthrough the aperture and then to automatically return to the unbiasedlocked position over a head of the inserted bone screw; and a springmount rotatably mounted in a recess of the base plate which is locatedadjacent to and intersects the aperture, the spring mount comprising anotch, wherein the proximal end of the split ring is retained within thenotch, and wherein when the spring mount is rotated, the split ring isalso rotated such that the curved portion of the split ring rotates awayfrom the head of the inserted bone screw to allow the inserted bonescrew to be removed for purposes of a revision surgery.
 2. The spinalplate assembly of claim 1, wherein when the spring mount is rotated, awall of the base plate aperture compresses the curved portion of thesplit ring into the notch of the spring mount to allow the inserted bonescrew to be removed.
 3. The spinal plate assembly of claim 1, whereinthe spring mount comprises a rotatable member including: a pin receivedin a bore within the recess of the base plate; and a head disposed onthe pin, the head comprising the notch for retaining the split ring. 4.The spinal plate assembly of claim 3, wherein the head includes a drivefeature adapted to be mated to a complementary drive feature of aremoval tool for rotation.
 5. The spinal plate assembly of claim 4,wherein the drive feature is slotted, square, triangular, rectangular,pentagonal, hexagonal, octagonal, n-lobular, hexalobular, stardrive, ortrilobular in shape.
 6. The spinal plate assembly of claim 3, whereinthe head is adapted to rotate about the pin.
 7. The spinal plateassembly of claim 3, wherein the pin is threadably received in the bore.8. The spinal plate assembly of claim 1, wherein: the base plateincludes at least two apertures each for receiving a bone screw; and therecess of the base plate and the spring mount are centrally disposedbetween the at least two apertures.
 9. A spinal plate assemblycomprising: a base plate defining an aperture comprising a seat forreceiving a bone screw; a deformable split ring having a proximal end, adistal end, and a curved portion, the split ring overlying the aperturein its unbiased locked position, the curved portion of the split ringadapted to be flexed radially inwardly and away from the aperturethrough contact with a head of the bone screw when the bone screw isbeing inserted through the aperture and then to automatically return tothe unbiased locked position over the inserted bone screw head to blockthe inserted bone screw; a spring mount rotatably mounted in a recess ofthe base plate which is located adjacent to and intersects the aperture,the spring mount comprising a circumferential groove for retaining atleast a portion of the split ring, and wherein when the spring mount isrotated, the split ring is also rotated in a same direction such thatthe curved portion of the split ring rotates and is compressed into therecess of the base plate to allow the inserted bone screw to be removedfor purposes of a revision surgery.
 10. The spinal plate assembly ofclaim 9, wherein a quarter turn of the spring mount rotates the curvedportion of the split ring and a wall of the base plate recess compressesthe curved portion of the split ring to allow the inserted bone screw tobe removed.
 11. The spinal plate assembly of claim 9, wherein the springmount comprises a rotatable member including: a pin received in a borewithin the recess of the base plate; and a head disposed on the pin, thehead comprising the circumferential groove for retaining the split ring.12. The spinal plate assembly of claim 11, wherein the head includes adrive feature adapted to be mated to a complementary drive feature of aremoval tool for rotation.
 13. The spinal plate assembly of claim 12,wherein the drive feature is slotted, square, triangular, rectangular,pentagonal, hexagonal, octagonal, n-lobular, hexalobular, stardrive, ortrilobular in shape.
 14. The spinal plate assembly of claim 11, whereinthe head is adapted to rotate about the pin.
 15. The spinal plateassembly of claim 11, wherein the pin is threadably received in thebore.
 16. The spinal plate assembly of claim 9, wherein: the base plateincludes at least two apertures each for receiving a bone screw; and therecess of the base plate and spring mount are centrally disposed betweenthe at least two apertures.
 17. The spinal plate assembly of claim 16,wherein the split ring comprises an elongate straight portion and twocurved portions each for locking a bone screw in a respective one of theat least two apertures of the base plate.